No-freeze refrigerant control



Sept. 29, 1964 c. L. TUCKER 3,150,502

NO-FREEZE REFRIGERANT CONTROL Filed July 25, 1962 E VAPORATOR COMPRESSOR 8 VALVE RESPONSIVE TO OUTLET PRESSURE CONDENSER INVENTOR. Carl L. Tucker BY ulf/J; AW/Z/ #01 ATTORNEYS United States Patent ,15 9 Nit-FREEZE REFRIGERANT CONTROL Carl L. Tucker, Skaneateles, N.Y., assignor, by mesne assignments, to The Singer Company, New York, N.Y., a corporation of New Jersey Filed July 25, 1962, Ser. No. 212,198 2 Claims. e1. 62-197 This invention relates to refrigeration, and more in particular to controlling the temperature of the evaporator in the refrigeration system of air conditioning units.

In hermetic refrigeration systems of the type which the form of capillary tubes. Sugh air conditioning units it is a common practice to cool the condenser with the outside air. Also, such refrigeration systems generally are provided with fixed expansion or restrictor means in the form of capillary tubes. Such air conditioning units are mounted in the walls of buildings or in adjacent windows and are used to maintain a desired temperature and humidity condition in an enclosure as well as provide ventilation.

In many such installations the air conditioning unit is operated throughout the year, or in any event the refrigeration system is used to cool the air in the room even when the outside temperature drops considerably below the room temperature to take care of a temperature condition in the enclosure resulting from a sun load or other cause. With such an operating condition and with a fixed restrictor or capillary tube, a drop in the outside temperature causes a corresponding drop in the condenser temperature and pressure and the evaporator temperature. Also suchunits normally draw in outside air for ventilation and when the temperature of that air is low the load on the refrigeration system is reduced so that the reduction in load may cause an even further reduction in the evaporator temperature. This mode of operation has produced problems because the evaporator temperature may drop below freezing and the condensate become frozen and accumulate on the evaporator in the form of frost or ice. Such an accumulation of frost and ice blocks the air passageways of the evaporator so that the air conditioning unit becomes ineffective in reducing the temperature and humidity within the room. The reduction in heat transfer between the air and the evaporator causes a further reduction in the evaporator temperature so that the continued operation of the refrigeration system maintains the accumulated frost at a low temperature.

It is an object of the present invention to provide an improved control in the refrigeration system for air conditioning units to overcome the difiiculties discussed above. Another object of this invention is to insure that the evaporator of a refrigeration system is maintained within a specific temperature range under all conditions of operation. I is a further object to provide an improved temperature control for refrigeration systems and thereby improve the air conditioning unit in which they are used. A further object is to provide for the above with apparatus which is thoroughly practical and is adaptable to varying conditions of operation and use. These and other objects will be in part obvious and in part pointed out below.

In the drawing the single figure is a schematic representation of one embodiment of the invention.

Referring to the drawing, a refrigeration system is illustrated which is particularly adapted for use in an air conditioning unit. The refrigeration system comprises a compressor 2 which discharges compressed refrigerant to a condenser 4 from which it passes through a line 6 to a capillary restrictor or expansion device 8 and thence through a line 10 to an evaporator 12. The evaporator 12, in turn, is connected by a line 13 to the suction side 3,159,592 Patented Sept. 29, 1964 of the compressor 12 to complete the refrigerant circuit and the compressor maintains the refrigerant in the evaporator at a low pressure and temperature. A single motor 14 drives an air circulating fan 16 which directs a stream of air through the evaporator 12 to recirculate air within the room and also to draw in and cool a stream of outside air for purposes of ventilation. Motor 14 also drives a fan 18 which directs a stream of outside air through condenser 4 thus to provide air cooling for the refrigeration system.

Connected between lines 6 and It in parallel with capillary tube 3 is a pressure-operated expansion valve 29. Hence, when valve 20 is open, the liquid refrigerant may flow in parallel paths through capillary tube 8 and valve 20. However, valve 20 is controlled by the pressure of the refrigerant in evaporator 12 and is open only when the evaporator pressure drops below that corresponding to a temperautre above freezing as, for example, 33 F. At evaporator temperatures above 33 F., all of the refrigerant passing to the evaporator flows through capillary tube 8. But at evaporator temperatures below 33 F., valve 20 opens and the evaporator receives an additional supply of liquid refrigerant. Valve 20 has no bleed port so that it has no eflect upon the operation at temperatures above 33 F.

The components and constructions of the air conditioning units are the same as those of a standard air conditioning unit except for the presence of valve 29. Therefore, the air conditioning unit operates to cool, dehumidify and ventilate in a conventional manner except when the pressure of the evaporator 12 drops below the pressure corresponding to a temperature of 33 F. At that pressure and temperature valve 29 opens so as to by-pass liquid refrigerant around capillary tube 3. The additional refrigerant passed through valve 20 causes an immediate increase in the evaporator pressure and temperature, and eliminates any tendency for frost or ice to be formed on the evaporator. Hence, the air conditioning unit continues to operate at a high capacity to cool and dehumidify the fresh and recirculated air and the condensate continues to drain from the evaporator. While valve 20 is of the type which is responsive to the low side pressure, it is understood that that pressure is related directly to the refrigerant temperature in the evaporator. It is contemplated that valve 26 may be made responsive to the evaporator fin temperature or to the ambient air temperature.

It will now be observed that the present invention provides an improved control for refrigeration systems used in an air conditioning unit to prevent cooling air below freezing temperatures. It will further be observed that the present invention provides an apparatus which is thoroughly practical and is adapted to varying conditions of operation and use.

While a single embodiment of the invention is herein illustrated and described, it will be understood that changes may be made in the construction and arrangement of elements without departing from the spirit or scope of the invention. Therefore, without limitation in this respect the invention is defined by the following claims.

I claim:

1. In a refrigeration system of the type having an evaporator wherein refrigerant is evaporated to cool air and a condenser wherein refrigerant is cooled and condensed by air and wherein there is a compressor which compresses refrigerant from the evaporator and delivers the compressed refrigerant to the inlet of the condenser and liquid refrigerant passes through a fixed restrictor forming the outlet from the condenser to the evaporator whereby a rise in the ambient temperature at the condenser causes an increase in the rate of flow of liquid refrigerant to the evaporator and a drop in said ambient temperature causes a decrease in said rate of flow of liquid refrigerant with the result that an extreme drop in said ambient temperature causes the temperature at the evaporator to drop below the freezing temperature and ice tends to form thereon, that improvement which comprises, an auxiliary expansion valve connected in parallel with said restrictor and being adapted to be opened to supply an auxiliary stream of liquid refrigerant from the outlet of the condenser to the evaporator and being adapted to close to cut off said auxiliary stream of liquid refrigerant, said auxiliary expansion valve including fluidpressure operating means which is operated in response to changes in the temperature and pressure of the refrigerant in the evaporator and which opens said auxiliary expansion valve when the pressure of the refrigerant in the evaporator drops below that corresponding to a temperature of the order of 33 F. at which ice may tend to form upon the evaporator surface, said operating means acting to close said auxiliary expansion valve at a pressure above that corresponding to a temperature of the order of 33 F., whereby said restrictor provides the sole supply of liquid refrigerant to the evaporator at temperatures above a temperature of the order of 33 F. below which the auxiliary stream of liquid refrigerant is supplied to the evaporator to prevent an excessive drop in the pressure of the refrigerant in the evaporator.

2. Apparatus as described in claim 1 wherein said refrigeration system is incorporated into an air conditioning unit and includes air circulating means to circulate air in heat-exchange relationship with said evaporator, and an electric motor for driving said air circulating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,891,357 Peltier Dec. 20, 1932 2,739,451 Break Mar. 27, 1956 2,742,768 Baer Apr. 24, 1956 2,777,297 Doeg Jan. 15, 1957 2,851,864 Webber Sept. 16, 1958 2,944,411 McGrath July 12, 1960 2,967,403 Lange et al. Jan. 10, 1961 3,041,845 Trask July 3, 1962 

1. IN A REFRIGERATION SYSTEM OF THE TYPE HAVING AN EVAPORATOR WHEREIN REFRIGERANT IS EVAPORATED TO COOL AIR AND A CONDENSER WHEREIN REFRIGERANT IS COOLED AND CONDENSED BY AIR AND WHEREIN THERE IS A COMPRESSOR WHICH COMPRESS REFRIGERANT FROM THE EVAPORATOR AND DELIVERS THE COMPRESSED REFRIGERANT TO THE INLET OF THE CONDENSER AND LIQUID REFRIGERANT PASSES THROUGH A FIXED RESTRICTOR FORMING THE OUTLET FROM THE CONDENSER TO THE EVAPORATOR WHEREBY A RISE IN THE AMBIENT TEMPERATURE AT THE CONDENSER CAUSES AN INCREASE IN THE RATE OF FLOW OF LIQUID REFRIGERANT TO THE EVAPORATOR AND A DROP IN SAID AMBIENT TEMPERATURE CAUSES A DECREASE IN SAID RATE OF FLOW OF LIQUID REFRIGERANT WITH THE RESULT THAT AN EXTREME DROP IN SAID AMBIENT TEMPERATURE CAUSES THE TEMPERATURE AT THE EVAPORATOR TO DROP BELOW THE FREEZING TEMPERATURE AND ICE TENDS TO FORM THEREON, THAT IMPROVEMENT WHICH COMPRISES, AN AUXILIARY EXPANSION VALVE CONNECTED IN PARALLEL WITH SAID RESTRICTOR AND BEING ADAPTED TO BE OPENED TO SUPPLY AN AUXILIARY STREAM OF LIQUID REFRIGERANT FROM THE OUTLET OF THE CONDENSER TO THE EVAPORATOR AND BEING ADAPTED TO CLOSE TO CUT OFF SAID AUXILIARY STREAM OF LIQUID REFRIGERANT, SAID AUXILIARY EXPANSION VALVE INCLUDING FLUIDPRESSURE OPERATING MEANS WHICH IS OPERATED IN RESPONSE TO CHANGES IN THE TEMPERATURE AND PRESSURE OF THE REFRIGERANT IN THE EVAPORATOR AND WHICH OPENS SAID AUXILIARY EXPANSION VALVE WHEN THE PRESSURE OF THE REFRIGERANT IN THE EVAPORATOR DROPS BELOW THAT CORRESPONDING TO A TEMPERATURE OF THE ORDER OF 33* F. AT WHICH ICE MAY TEND TO FORM UPON THE EVAPORATOR SURFACE, SAID OPERATING MEANS ACTING TO CLOSE SAID AUXILIARY EXPANSION VALVE AT A PRESSURE ABOVE THAT CORRESPONDING TO A TEMPERATURE OF THE ORDER OF 33* F., WHEREBY SAID RESTRICTOR PROVIDES THE SOLE SUPPLY OF LIQUID REFRIGERANT TO THE EVAPORATOR AT TEMPERATURES ABOVE A TEMPERATURE OF THE ORDER OF 33* F. BELOW WHICH THE AUXILIARY STREAM OF LIQUID REFRIGERANT IS SUPPLIED TO THE EVAPORATOR TO PREVENT AN EXCESSIVE DROP IN THE PRESSURE OF THE REFRIGERANT IN THE EVAPORATOR. 